Look up accuracy, precision in Wiktionary, the free dictionary.

In the fields of science, engineering, industry and statistics, accuracy is the degree of conformity of a measured or calculated quantity to its actual (true) value. Accuracy is closely related to precision, also called reproducibility or repeatability, the degree to which further measurements or calculations show the same or similar results. The results of calculations or a measurement can be accurate but not precise; precise but not accurate; neither; or both. A result is called valid if it is both accurate and precise. The related terms in surveying are error (random variability in research) and bias (non-random or directed effects caused by a factor or factors unrelated by the independent variable). Three Imaginary Boys is English rock band The Cures debut album. ... Wikipedia does not have an article with this exact name. ... Wiktionary (a portmanteau of wiki and dictionary) is a multilingual, Web-based project to create a free content dictionary, available in over 150 languages. ... Part of a scientific laboratory at the University of Cologne. ... Engineering is the applied science of acquiring and applying knowledge to design, analysis, and/or construction of works for practical purposes. ... This article is about the field of statistics. ... Conformity is the act of consciously maintaining a certain degree of similarity (in clothing, manners, behaviors, etc. ... In mathematics the concept of a measure generalizes notions such as length, area, and volume (but not all of its applications have to do with physical sizes). ... Quantity is a kind of property which exists as magnitude or multitude. ... Value in mathematics refers to the quantity that is represented by a variable. ... In Wikipedia, precision has the following meanings: In engineering, science, industry and statistics, precision characterises the degree of mutual agreement among a series of individual measurements, values, or results - see accuracy and precision. ... This article is in need of attention from an expert on the subject. ... This page is a candidate to be moved to Wiktionary. ... Various meters Measurement is an observation that reduces an uncertainty expressed as a quantity. ... A result is the final consequence of a sequence of actions or events (broadly incidents and accidents) expressed qualitatively or quantitatively, being a loss, injury, disadvantage, advantage, gain, victory or simply a value. ... Various meters Measurement is an observation that reduces an uncertainty expressed as a quantity. ... Statistical surveys are used to collect quantitative information about items in a population. ... Random redirects here. ... In an experimental design, the independent variable (argument of a function, also called a predictor variable) is the variable that is manipulated or selected by the experimenter to determine its relationship to an observed phenomenon (the dependent variable). ...

Accuracy vs precision - the target analogy

High accuracy, but low precision

High precision, but low accuracy

Accuracy is the degree of veracity while precision is the degree of reproducibility. The analogy used here to explain the difference between accuracy and precision is the target comparison. In this analogy, repeated measurements are compared to arrows that are fired at a target. Accuracy describes the closeness of arrows to the bullseye at the target center. Arrows that strike closer to the bullseye are considered more accurate. The closer a system's measurements to the accepted value, the more accurate the system is considered to be. Image File history File links High_accuracy_Low_precision. ... Image File history File links High_accuracy_Low_precision. ... Image File history File links High_precision_Low_accuracy. ... Image File history File links High_precision_Low_accuracy. ... Analogy is both the cognitive process of transferring information from a particular subject (the analogue or source) to another particular subject (the target), and a linguistic expression corresponding to such a process. ... An arrow is a pointed projectile that is shot with a bow. ... A bullseye on a dartboard. ...

To continue the analogy, if a large number of arrows are fired, precision would be the size of the arrow cluster. (When only one arrow is fired, precision is the size of the cluster one would expect if this were repeated many times under the same conditions.) When all arrows are grouped tightly together, the cluster is considered precise since they all struck close to the same spot, if not necessarily near the bullseye. The measurements are precise, though not necessarily accurate.
Further example, if a measuring rod is supposed to be ten yards long but is only 9 yards, 35 inches measurements can be precise but inaccurate. The measuring rod will give consistently similar results but the results will be consistently wrong.

However, it is not possible to reliably achieve accuracy in individual measurements without precision — if the arrows are not grouped close to one another, they cannot all be close to the bullseye. (Their average position might be an accurate estimation of the bullseye, but the individual arrows are inaccurate.) See also Circular error probable for application of precision to the science of ballistics. In the military science of ballistics, Circular Error Probability or circular error probable (CEP) is a simple measure of a weapon systems precision. ... Ballistics (gr. ...

Accuracy and precision in logic level modeling and IC simulation

As described in the SIGDA Newsletter [Vol 20. Number 1, June 1990] a common mistake in evaluation of accurate models is to compare a logic simulation model to a transistor circuit simulation model. This is a comparison of differences in precision, not accuracy. Precision is measured with respect to detail and accuracy is measured with respect to reality. Another reference for this topic is "Logic Level Modelling", by John M. Acken, Encyclopedia of Computer Science and Technology, Vol 36, 1997, page 281-306.

Quantifying accuracy and precision

Ideally a measurement device is both accurate and precise, with measurements all close to and tightly clustered around the known value. The accuracy and precision of a measurement process is usually established by repeatedly measuring some traceable reference standard. Such standards are defined in the International System of Units and maintained by national standards organizations such as the National Institute of Standards and Technology. Traceability refers to the completeness of the information about every step in a process chain. ... Look up si, Si, SI in Wiktionary, the free dictionary. ... A standards organization, also sometimes referred to as a standards body, a standards development organization or SDO (depending on what is being referenced), is any entity whose primary activities are developing, coordinating, promulgating, revising, amending, reissuing, interpreting, or otherwise maintaining standards that address the interests of a wide base of... NIST logo The National Institute of Standards and Technology (NIST, formerly known as The National Bureau of Standards) is a non-regulatory agency of the United States Department of Commerce’s Technology Administration. ...

Precision is usually characterised in terms of the standard deviation of the measurements, sometimes called the measurement process's standard error. The interval defined by the standard deviation is the 68.3% ("one sigma") confidence interval of the measurements. If enough measurements have been made to accurately estimate the standard deviation of the process, and if the measurement process produces normally distributed errors, then it is likely that 68.3% of the time, the true value of the measured property will lie within one standard deviation, 95.4% of the time it will lie within two standard deviations, and 99.7% of the time it will lie within three standard deviations of the measured value. Image File history File links No higher resolution available. ... In probability and statistics, the standard deviation of a probability distribution, random variable, or population or multiset of values is a measure of the spread of its values. ... The standard error of a method of measurement or estimate is the estimated standard deviation of the error in that method. ... In this diagram, the bars represent observation means and the red lines represent the confidence intervals surrounding them. ...

This also applies when measurements are repeated and averaged. In that case, the term standard error is properly applied: the precision of the average is equal to the known standard deviation of the process divided by the square root of the number of measurements averaged. Further, the central limit theorem shows that the probability distribution of the averaged measurements will be closer to a normal distribution than that of individual measurements. A central limit theorem is any of a set of weak-convergence results in probability theory. ... In mathematics and statistics, a probability distribution is a function of the probabilities of a mutually exclusive and exhaustive set of events. ...

With regard to accuracy we can distinguish:

• the difference between the mean of the measurements and the reference value, the bias. Establishing and correcting for bias is necessary for calibration.
• the combined effect of that and precision.

A common convention in science and engineering is to express accuracy and/or precision implicitly by means of significant figures. Here, when not explicitly stated, the margin of error is understood to be one-half the value of the last significant place. For instance, a recording of 843.6m, or 843.0m, or 800.0m would imply a margin of 0.05m (the last significant place is the tenths place), while a recording of 8436 m would imply a margin of error of 0.5m (the last significant digits are the units). In statistics, mean has two related meanings: the arithmetic mean (and is distinguished from the geometric mean or harmonic mean). ... In statistics, the difference between an estimators expected value and the true value of the parameter being estimated is called the bias. ... Calibration refers to the process of determining the relation between the output (or response) of a measuring instrument and the value of the input quantity or attribute, a measurement standard. ... Rounding to n significant figures is a form of rounding. ...

A reading of 8000m, with trailing zeroes and no decimal point, is ambiguous; the trailing zeroes may or may not be intended as significant figures. To avoid this ambiguity, the number could be represented in scientific notation: '8.0 x 10³m' indicates that the first zero is significant (hence a margin of 50m) while '8.000 x 10³m' indicates that all three zeroes are significant, giving a margin of 0.5m. Similarly, it is possible to use a multiple of the basic measurement unit: '8.0 km' is equivalent to '8.0 x 10³ m'. In fact, it indicates a margin of 0.05 km (50 m). However, reliance on this convention can lead to false precision errors when accepting data from sources that do not obey it. This article or section does not cite its references or sources. ...

Looking at this in another way, a value of 8 would mean that the measurement has been made with a precision of '1' (the measuring instrument was able to measure only up to 1's place) whereas a value of 8.0 (though mathematically equal to 8) would mean that the value at the first decimal place was measured and was found to be zero. (The measuring instrument was able to measure the first decimal place.) The second value is more precise. Neither of the measured values may be accurate (the actual value could be 9.5 but measured inaccurately as 8 in both instances). Thus, accuracy can be said to be the 'correctness' of a measurement, while precision could be identified as the ability to resolve smaller differences.

Precision is sometimes stratified into:

• Repeatability - the variation arising when all efforts are made to keep conditions constant by using the same instrument and operator, and repeating during a short time period; and
• Reproducibility - the variation arising using the same measurement process among different instruments and operators, and over longer time periods.

A common way to statistically measure precision is a Six Sigma tool called ANOVA Gage R&R. As stated before, you can be both accurate and precise. For instance, if all your arrows hit the bull's eye of the target, they are all both near the "true value" (accurate) and near one another (precise). This page is a candidate to be moved to Wiktionary. ... This article is in need of attention from an expert on the subject. ... The often-used six sigma symbol. ... There are very few or no other articles that link to this one. ...

Something to think about: In the NFL, a place kicker makes 9 of 10 field goals, and another makes 6 of 10. Even if the 6 that the second kicker made were straight down the middle and the first kicker just made his in, he is still less accurate and less precise than the first kicker. This differs from the darts example because either you make it or you do not; there are not different levels of points that can be scored.

Accuracy in biostatistics

"Accuracy" is also used as a statistical measure of how well a binary classification test correctly identifies or excludes a condition. Binary classification is the task of classifying the members of a given set of objects into two groups on the basis of whether they have some property or not. ...

That is, the accuracy is the proportion of true results (both true positives and true negatives) in the population. It is a parameter of the test. The sensitivity of a binary classification test or algorithm, such as a blood test to determine if a person has a certain disease, or an automated system to detect faulty products in a factory, is a parameter that expresses something about the tests performance. ... The specificity is a statistical measure of how well a binary classification test correctly identifies the negative cases, or those cases that do not meet the condition under study. ... Scientists recognize two different sorts of error:[1] Statistical error: the difference between a computed, estimated, or measured value and the true, specified, or theoretically correct value (see errors and residuals in statistics) that is caused by random, and inherently unpredictable fluctuations in the measurement apparatus. ... Scientists recognize two different sorts of error:[1] Statistical error: the difference between a computed, estimated, or measured value and the true, specified, or theoretically correct value (see errors and residuals in statistics) that is caused by random, and inherently unpredictable fluctuations in the measurement apparatus. ...

An accuracy of 100% means that the test identifies all sick and well people correctly.

Also see Specificity (tests) and Sensitivity (tests). The specificity is a statistical measure of how well a binary classification test correctly identifies the negative cases, or those cases that do not meet the condition under study. ... The sensitivity of a binary classification test or algorithm, such as a blood test to determine if a person has a certain disease, or an automated system to detect faulty products in a factory, is a parameter that expresses something about the tests performance. ...

Accuracy may be determined from Sensitivity and Specificity, provided Prevalence is known, using the equation:

accuracy = (sensitivity)(prevalence) + (specificity)(1 − prevalence)

Accuracy and precision in psychometrics

In psychometrics the terms accuracy and precision are interchangeably used with validity and reliability respectively. Validity of a measurement instrument or psychological test is established through experiment or correlation with behavior. Reliability is established with a variety of statistical technique (classically Cronbach's alpha). In psychology, validity has two distinct fields of application. ... In statistics, reliability is the consistency of a set of measurements or measuring instrument. ... Cronbachs (alpha) has an important use as a measure of the reliability of a psychometric instrument. ...

References

• Accuracy and Precision